sedimentary
Banded Iron Formation (BIF)
Banded Iron Formation (Magnetite-Hematite-Chert)
Hardness: 5-7 (Mohs); Color: Dark gray to black bands with reddish-brown oxidation; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0 (heavy due to iron content)
- Hardness
- 5-7 (Mohs)
- Color
- Dark gray to black bands with reddish-brown oxidation
- Luster
- Sub-metallic to dull
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Physical properties
Hardness: 5-7 (Mohs); Color: Dark gray to black bands with reddish-brown oxidation; Luster: Sub-metallic to dull; Crystal structure: Microcrystalline; Specific gravity: 3.0-5.0 (heavy due to iron content)
Formation & geological history
Formed in Paleo-Proterozoic oceans (2.4 to 1.8 billion years ago) through the precipitation of iron and silica as atmospheric oxygen levels rose due to photosynthesis (The Great Oxygenation Event).
Uses & applications
Primary source of iron ore for steel production and industrial manufacturing globally. Smaller pieces are used as decorative lapidary material.
Geological facts
These formations provide the definitive evidence for the rise of life on Earth, as the iron only precipitated once ancient cyanobacteria started producing oxygen as a waste product.
Field identification & locations
Identify by its heavy weight, dark metallic bands, and magnetic properties if magnetite is present. Commonly found in ancient cratons like the Superior Upland, Western Australia, and Brazil.
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